Tree & Shrub Establishment
In many parts of the country, fall is promoted as a good time to plant trees and shrubs. Although this is true, the timing of tree and shrub planting is not as critical as using the proper planting techniques. Many people joke that all you need to do is dig a hole and position the plant green side up. On the contrary, research over the past 20 years shows that the planting process is far more sophisticated than that if you want to be confident of planting success.
Professionals may plant almost any time of the year, depending on the region. However, winter may be impractical due to frozen ground, and summer places heavy water demands on the transplant, requiring extra attention to irrigation. Thus, spring and fall are the preferred times to transplant due to the moderate weather during these seasons.
PLANTING HOLE PREPARATION
Trees and shrubs require similar planting procedures. For trees, dig shallow planting holes that are two to three times as wide as the root ball or root spread. For shrubs, dig similar holes. Another option is to rotary till the entire shrub planting bed, then dig holes slightly larger than the root balls or root spread. Wide, shallow holes encourage the horizontal root growth that trees and shrubs normally produce.
Planting-hole depth depends on the drainage conditions. In well-drained soils, dig holes as deep as the root balls. In poorly drained soils, dig holes 1 to 2 inches shallower than the root balls, covering the exposed root-ball tops with mulch.
Do not dig planting holes any deeper than the root-ball depths. Otherwise, you will have to put soil back into the hole beneath the root balls. Loose soil will compact over time. Your trees and shrubs then will sink, causing them to be planted too deeply. In addition, slow-draining water from the bottom of the planting hole can damage their roots.
Whenever possible, you should widen the tops of your planting holes. Doing so will increase the well-aerated soil area near the surface where most root growth occurs. Also, take time to score walls of machine-dug holes to eliminate glazing, particularly in clay soils.
TREE AND SHRUB PREPARATION
Placing the plant in the planting hole is simple for container-grown or bare-root specimens. For larger specimens, such as B&B or box trees, it is a bit more demanding. Use anything that will allow you to lower the root ball into the hole without disturbing the roots. It is tempting to use the trunk, but this risks other harm to the tree. Instead, use ropes to lower the root ball into the hole or boards on which you can slide the root ball. If the tree comes in a wire basket, use the wire hoops as grips. Heavy, large specimens may require a small crane or hoist.
The wrapping material around a root ball, or the container in which it has grown, can cause problems. Growers often use synthetic materials that don’t degrade or treated burlap that degrades slowly. In addition, the ropes that tie or lash the balls are often non-degradable materials. With B&B trees and shrubs, inspect the wrapping materials around root balls and cut or remove any non-degradable material. However, do so only after the tree is situated in its final position within the planting hole. Other factors to consider are:
- Ball-pinning nails and ropes. Cut away as much wrapping material as possible, or drop the wrapping material to the bottom of the planting hole, eventually backfilling over it.
- Wire baskets. These can be a problem because they rust away slowly underground. To keep equipment from being caught in the top loops during future landscaping— and to keep surface roots from girdling—cut 8 to 12 inches off the top of all baskets.
- Plastic containers. Remove all plastic containers. If available, select trees grown in containers with vertical ribs or copper-treated interior walls. These types of containers minimize circling roots.
- Fiber pots. Break away the top portion of the pot or remove the pot entirely from trees and shrubs. Many fiber pots are coated or compressed to extend their shelf life, but such techniques slow degradation below ground and retard root extension.
- Root pruning. Cut dead, diseased or broken roots back to healthy tissue. Also, either remove or straighten circling roots or those matted in the bottom of the container. Planting is the time to eliminate roots that might cause girdling later on.
Straightening some of the per-ipheral roots so they extend a few inches into the backfill will aid the plant’s establishment. These roots will grow more easily than those that must grow out of an undisturbed root ball.
When you plant bare-root specimens, build a cone of soil in the bottom of the planting hole. Then spread the roots out over the soil cone (see Figure 1, page 29).
Take care to ensure that tree trunks are straight when you position them in the hole. If you are planting a budded tree, face the bud toward the afternoon sun. This will shade the inside curve above the bud, which may be sensitive to excessive sunlight and heat. White paint on this area can be helpful for sensitive species.
Another factor to consider when positioning trees or shrubs is crown symmetry. Orienting the less-developed side of the crown toward the sunniest exposure will encourage it to grow more quickly and balance out the crown over time.
Once you dig the holes and position and prepare the tree or shrub root balls, backfill the planting holes with the existing unamended soil. Do not incorporate organic matter or sand into backfill soil for individual planting holes because doing so will create differences in soil-pore sizes. Pore-size differences cause problems with water movement and root growth between the root ball, the backfill and the surrounding soil.
Do not backfill the entire planting hole in one operation. Backfill half the soil, then water thoroughly to settle out air pockets and re-moisten the soil in the root ball. Finish backfilling and water again.
You can add fertilizer as you backfill, provided you use a slow-release form (resin- or sulfur-coated, briquette or compressed) at a low rate (1 pound of actual nitrogen per 1,000 square feet of planting-hole surface area). Avoid using fast-release agronomic fertilizers (such as ammonium nitrate) because these can dehydrate tree and shrub roots if you apply too much.
Once you complete backfilling and watering, decide if you want to apply a surface treatment for weed control. Your primary options include mulch, landscape fabric or pre-emergence herbicides—alone or in combinations.
- Mulch. Availability, appearance, weed-suppression capabilities and cost determine what type of mulch product to use—organic or inorganic. Most landscapers prefer organic mulches for appearance, moisture conservation and organic-matter replenishment of the soil. However, inorganic mulches better resist decomposition.
Apply no more than 2 to 4 inches of mulch. Use more of materials with large particle size to form a light barrier that inhibits weed-seed germination. Keep mulches from touching tree and shrub stems to reduce moisture damage and rodent feeding (when using organic mulches) and bark abrasion (when using inorganic mulches).
- Physical barriers. If you use a physical barrier with your mulch, do not use solid plastic. It blocks important moisture and gas exchange between the soil and atmosphere. Instead, use one of the porous woven or non-woven synthetic geotextiles or landscape fabrics.
- Pre-emergence herbicides. Select your herbicide based on the major species of weeds you have to control. The label should list the herbicide as safe for the tree and shrub species around which you’ll apply the material. Also, be sure that your rate and timing are correct for maximum effectiveness. If you use a mulch in addition to a pre-emergence herbicide, apply the mulch first, then the herbicide.
STAKING AND OTHER SUPPORTS
Shrubs seldom require staking. Trees, however, often require added support until their trunks grow and strengthen. Further, you may need to supply physical protection for a transplant vulnerable to vandalism, mower damage or some other hazard. Here are some of the common methods of supporting and protecting trees:
- Anchor staking. Staking to anchor the root ball is helpful in windy locations or areas where the tree will be prone to disturbance. Roots growing from the root ball into the surrounding soil may break if you allow too much movement. Therefore, many arborists use anchor stakes to prevent such movement. These consist of short stakes, usually two or three, in firm ground just outside the root ball. These are attached low on the trunk with wire and soft wrap material to protect the trunk (see Figure 2, page 30). One year is usually adequate time for anchor staking.
- Support staking. Staking for trunk and crown support is not necessary for most shrubs and many trees. You should leave those that clearly are self-supporting unstaked. However, many trees, especially container-grown specimens, have spindly trunks, and you must stake them until they develop sufficient trunk size.
Tying trees rigidly to one stake is not a proper way to stake trees, even though many container plants come from the nursery in this state. Trees treated this way are not able to develop thickened trunks with any speed and often develop wounds from friction with the stake.
A better method is to use one or two stakes several inches away from the trunk. From near the top of the stakes, you can run wire to the trunk in a figure-eight arrangement (see Figure 3, page 30). To determine where to tie to the trunk, grasp the trunk, deflect the crown slightly and see if it rights itself. Tie to the trunk about 6 inches above the lowest grasping point that allows the crown to return to an upright stance. You must use a soft material to protect the trunk from damage from the wire. Landscapers often use cut sections of rubber garden hose, but even this can cause trunk injury. Suppliers carry cloth, polyethylene or other tie material manufactured for this purpose, and these provide adequate support with minimal risk of trunk injury. Wood is the most common stake material, but metal stakes are adequate, though not always as attractive.
Staking may be necessary for 1 or more years, depending on the growth rate of the tree and the taper of the trunk. Therefore, you must use your judgment when deciding when to remove the stakes. As soon as the tree is self-supporting, remove the staking. However, you may wish to leave the stakes in place for physical protection of the trunk.
- Guying. This involves running cord or cable from stakes near ground level to a point (see subheading, “Support staking,” above Figure 4 at left, to determine tie location) higher up on the trunk (see Figure 4, at 31). Arborists use guying more often with large transplants, but it may succeed for smaller transplants as well. Though guying is an acceptable alternative to staking, it requires the same precautions. For example, use material that won’t wound the trunk, and tie the guy lines loosely enough to allow the tree some room to flex and move with the wind.
- Protective staking. Depending on the site, you may wish to install stakes to provide trunk protection for a newly planted tree. These usually consist of nothing more than two or three stakes 1 to 2 feet from the trunk. They should be tall enough to provide protection from whatever hazard is likely to be present— mowers, for example.
Landscape professionals have devised many other ingenious support-staking schemes. The important factors are:
Tie to the trunk at the proper height.
Allow enough flexibility and movement to encourage the trunk to thicken and become self-supporting.
Do not use materials that could wound the tree’s trunk.
Remove staking or guying as soon as the tree is self-supporting.
Other structures, such as for protection, may be appropriate in certain situations. These could include extensive protective structures for preventing vandalism or animal damage, or metal grating over the root-ball area to prevent traffic damage to a young root system. Large palm trees require bracing with boards to keep their trunks upright until roots become established (see Figure 5, page 31).
Needless to say, desiccation is the greatest threat to newly planted trees and shrubs. Therefore, irrigation is the most critical need of transplants until they establish root systems well beyond their original root ball. Newly planted trees and shrubs vary in their water requirements. Bare-root plants should not need irrigation (aside from watering at planting time) until at least 2 weeks after growth commences. At the other end of the scale, plants in full leaf may need daily irrigation during warm weather.
The goal of watering a new transplant is to keep the root ball and the surrounding backfill adequately moist. However, the danger of overwatering and creating a “bathtub” in the planting hole, especially in tight soils, is a real one. Some plants—for example, palm trees—are extremely sensitive to overwatering. At planting, many landscapers build a berm around the perimeter of the planting hole to create a water basin. To minimize the risk of overwatering, construct a smaller berm within the larger one—just outside the root ball and high enough to hold enough water to re-wet the root ball (see Figure 6, page 32). Filling this smaller basin daily with water will keep the root ball and a bit of the surrounding backfill moist. Irrigate the larger basin every 2 or 3 weeks.
After the first few days of irrigating the inner basin, lengthen the watering interval until the first signs of wilting appear. Then adjust the watering interval so that it is one day shorter than the length of time in which wilting occurs. Continue on this schedule for a few weeks. Then readjust the watering frequency again, using the same method. You can gradually cut back watering frequency in this way.
You can apply water in various ways. Hand watering is most common for new transplants, but drip works well too. Other systems, such as water-filled plastic bags you lay around the trunk, also perform well. The important point is that no irrigation system eliminates the need to keep track of the amount of water you apply. You must keep the root ball and surrounding backfill wetted but not constantly saturated.
A FEW FINAL PLANTING NOTES
- Pruning. Do not prune off one-quarter to one-third of the stem and leaf growth as was once recommended. Newly transplanted trees and shrubs need the growth regulating hormone auxin, which is made by the terminal buds, and the sugar made by the leaves for root growth. Limit structural pruning to removing problems—multiple leaders, narrow crotch (branch-attachment) angles, water sprouts, basal suckers, and dead or infested branches. See Chapter 11 for more information on training young trees.
An exception to this rule is palm trees. Many species of large transplanted palms ideally should have all of their fronds removed to reduce water loss during establishment. Aesthetic considerations discourage this, however. At a minimum, though, remove the lower one-half of the fronds. Tie the remaining fronds up with degradable twine. This protects the apical bud during transplanting and reduces water loss until the twine degrades after a few months and releases the fronds.
Based on the tree’s environment, decide whether to apply a wrap or guard to its trunk. Consider these options for specific tree-planting sites:
- Wraps. They can be beneficial in heat sinks, such as tree islands in parking lots. A white wrap, which reflects heat, is beneficial if you transplant your tree during the spring or summer. Be sure the wrap doesn’t stay on the tree trunk for more than a year. Don’t attach the wrap with wire, electrical tape, plastic ties, nylon rope or other materials that have no give and resist decomposition.
- Guards. If tree trunks need physical protection from equipment, animals or people, use a guard that doesn’t touch the trunk and permits air circulation. Guards serve a function similar to protective staking but may not prevent equipment from bumping the tree, depending on the product. Coiled plastic guards that unfurl to fit the tree’s trunk are inexpensive and effective protection from trimmer damage—an all-too-common cause of injury for young trees. If the guard will be in place for multiple years, be sure to periodically inspect it and loosen it if necessary to keep it from damaging an ever-widening trunk.
It is important to remove all tags and labels from trees and shrubs to prevent girdling of branches and trunks.